a. Field of Invention
The invention relates generally to a rollover vent valve, including a rollover vent valve that is capable of preventing liquid carry-over during dynamic conditions.
b. Description of Related Art
Fuel level responsive vent valves are conventionally used in automobile fuel tanks. Vent valves may be located in the fuel tank to remain open when the fuel is below a certain level, and to close when the fuel reaches the valve. Two common applications of these valves are “rollover” valves, which respond to abnormal fuel levels or unusual vehicle angles to close a vapor outlet from the tank, and fuel shutoff or “fill control” valves which are positioned to close when the fuel tank reaches the “full” level during refueling.
In order to provide protection against fuel spilling from the vapor vent line in a fuel tank in the event of vehicle rollover, motor vehicle fuel tanks are generally equipped with valves which close the vapor vent when the vehicle is tilted beyond a threshold amount from the normal upright position. Such rollover/vent valves conventionally employ a float which closes the valve when the liquid level of the fuel rises above a predetermined level in order to prevent liquid fuel from sloshing out of the vapor vent either during normal operation or in the event of rollover. Generally, the valve may be located at the highest portion or the location of the deepest fuel level in order to provide vapor venting at all levels of fuel up to the maximum fuel level.
Rollover vent valves may vent fuel vapor from a vehicle fuel tank to the atmosphere or to a vapor recovery system, such as a carbon canister. Such valves typically vent the interior of the fuel tank to the carbon canister when the fuel in the tank is below the level of the valve, and are closed by a float when the fuel surges in a rollover situation. Closing the valve in response to surging liquid fuel level prevents the overflow of liquid fuel into the carbon canister. If employed as a fill-control vent valve, rather than rollover vent valve, closure is in response to a full fuel level rather than surge and results in a pressure head within the fuel tank and filler pipe to operate automatic shutoff apparatus built into the fuel fill nozzle.
Rollover vent valves are generally used to discriminate vapor from liquid. The valve may provide for flow of vapor in the presence of vapor and prevent liquid flow in the presence of liquid, and may do so under various conditions. Conventional rollover vent valves may perform this function at various degrees of effectiveness under static conditions. Under static conditions, conventional rollover vent valves may use a float and spring mechanism that is biased to closed in the presence of the liquid buoyant force. The float may be designed to be heavier than the spring force, so that the float may move to the open position when it is not in the presence of a liquid.
A need remains for a vent valve that is capable of preventing liquid carry-over during dynamic conditions.